Improved aerodynamics for motor vehicles are leading to future windshield designs with more pronounced rake angles, which produce a larger window surface. A window wiper system for such windshields must therefore include longer, more massive wiper arms and blades to wipe the required percentage of the larger surface. In a symmetrical overlap wipe pattern, in which the blades are oscillated in opposing movement between separated outer wipe positions and an overlapping inner wipe arrangement, longer arms and blades produce a larger overlap or collision avoidance region and, consequently, a need for increased blade separation.
Present symmetrical overlap wiper systems use a single motor with an unbalanced linkage to move the wiper blades through a repeating pattern, with one of the blades always overlapping the other in an overlapping inner wipe arrangement. The overlapping blade leads the other from the overlapping inner wipe arrangement through the overlap region toward its outer wipe position and follows the other back through the overlap region into the overlapping inner wipe arrangement. It must therefore pause at its outer wipe position to allow the other blade time to reach its outer wipe position and return so the other blade can precede it back into the overlap region. When the paused blade is restarted, it must be rapidly accelerated to make up for the time lost in the pause in order to achieve high wipe rates such as 75 wipes per minute; and this rapid acceleration of a large mass puts extra stress on the linkage components and may lead to an undesired whipping action of the blade end.